Boonton PIM 31 User Manual Manual de usuario descargar pdf (Pagina 77)

11 What is PIM?

PIM distortion is caused by non-linear mixing of two or more frequencies in

passive devices like cables and connectors. Ideal passive devices are

considered linear. In reality any linear component has a non-linear factor that can

cause PIM distortion. For optimal operation of RF systems, PIM has to be kept at

a very low level that has virtually no influence on the network operation. PIM

signals are generally unwanted because they can interfere with signals in a

receive path.

11.1 What Causes PIM?

Passive intermodulation can be caused by a variety of factors. PIM distortion is

often the result of flaws in component design and manufacturing processes. PIM

distortion may also be caused by wear and tear on components due to

mechanical constraints or environmental conditions.

11.1.1 Manufacturing & Design

• Use of ferromagnetic materials, such as nickel or steel, within the current

path. Especially at higher power levels, PIM can be generated due to

hysteresis effect of these materials and the non-linear voltage to current

ratio.

• Contaminations, like particles from machining operations or soldering

splatters that touch current carrying surfaces.

• Separation of current carrying contact zones through irregular contact

surfaces, corrosion and insufficient contact pressure.

• Dissimilar metals at contact areas.

• Insufficient thickness of plated metal causing RF heating through the skin

effect of RF.

• Bad solder joints.

11.1.2 Mechanical

• Poor mechanical alignment of components

• Too much or too little torque at connections

• Contaminated connectors

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Boonton PIM 31 User Manual Manual de usuario Pagina 77